In copending application Ser. No. 346,880, filed Feb. 8, 1982 of the inventor of the instant application, it was proposed to insulate mutually, in interwound coils with increasingly heavily insulated shell or casing surfaces, at least two turns, respectively, in the input region, at the inner and outer rim additionally so that one edge is surrounded angularly by this supplemental insulation and the turn capacity between turns with normal insulation is greater than between turns with supplemental insulations.
By this arrangement, the field intensity in the most highly stressed oil wedges or corners between the edge turns and the adjacent turns is shifted away from the conductor by lining with solid insulation and reaches the order of magnitude of the field intensity at the more highly insulated edges at the casing surface. The formed rings thereby introduced, for example, with U or L-shaped cross section, represent a relatively great expense which is justified only for very high voltages. This is true also if the formed rings are made by additionally covering or encasing the winding conductors with insulating paper and surrounding the edge conductors on all sides.
With voltages which are not so extremely high, the stress of the edge insulation at the casing surface of the winding may already be lower than the stress by the voltage between adjacent turns in high-voltage windings without additionally insulated casing surfaces. Also thereby great reliability against longitudinal breakdowns as well as the reliability achieved primarily by the normal insulation of the conductors against breakdowns between adjacent turns is adjustable by the supplemental insulation according to the aforementioned earlier patent application of the inventor of the instant application. The construction of the supplemental insulation out of formed rings, however, is relatively even more expensive than in windings with increased insulation on the cylinder surfaces.
It is therefore an object of the invention to provide, for high voltage windings of disc coils in transformers with and without increased insulation of the shell or casing surfaces of the winding, an arrangement and design of disc(flat) coils, wherein the safety or reliability of the insulation against longitudinal sparkovers over several disc coils is somewhat equal to the safety or reliability of the turn insulation against breakdowns, without incurring appreciable additional costs.